1. Field of the Invention
This invention relates in general to motion detecting devices; and, more particularly, in a four wheel drive vehicle wherein unintended engagement of the front driving axle during vehicle use will result in damage to the vehicle drive train, an apparatus for sensing and indicating the status of the front driving axle without requiring the vehicle occupants to stop the vehicle and perform a visual inspection of the vehicle drive train.
2. Description of the Related Art
The four-wheel drive vehicle was developed toward the end of World War II to meet a special goal. The military found that working in loose traction terrain with heavy payloads meant getting stuck with great frequency and certainty. This was especially true with a conventional, single axle that allowed a truck to bury its axle while the rear wheels spun their way to the netherworld.
One of the solutions to this problem was to employ a pulling front axle with a pushing rear axle. Thus was born the first four-wheel drive vehicle.
In general terms, a four-wheel drive vehicle incorporates a solid, hypoid drive with turning knuckles for steering. The steering knuckles are examples of mechanical complexity due to the fact that a flexible axle shaft joint, a sealed lubrication method and a drive mechanism to the wheel hub are required for four-wheel drive.
To distribute the power from the engine to the wheels, transfer cases and power dividers acting as gearboxes are used in the drive train system. Although some recent advances in four-wheel drive systems attempt to use automatic transmission-type planetary gearsets and chain drive mechanisms, the vast majority of existing and manufactured four-wheel drive vehicles remain all gear linked, from the transmission, through the transfer case, to the axle assemblies.
Most four-wheel drive vehicles are dual purpose utility vehicles. Driven daily on the street or long stretches over paved highways, they perform just like the ordinary two-wheel-drive vehicle. Unless the vehicle encounters terrain that requires four-wheel drive for traction, such as ice, loose gravel or snow, the transfer case of the vehicle drive train remains disengaged and the vehicle remains in two-wheel drive. It is when the driver of the vehicle requires four-wheel drive from the vehicle that a manual activation of the transfer case is made and the vehicle shifts into four-wheel drive.
The shift from two-wheel drive to four-wheel drive usually does not call for stopping the vehicle.
The most important requirement in operating a vehicle with a four-wheel drive is that the four-wheel drive must never be used on a hard, dry surface. The front axle will work against the rear, without slippage, especially on turns, and the result would be binding of the geartrain pieces and the damage of internal geartrain components.
A limited slip differential mechanism may be developed to provide a limited amount of slip to compensate for the speed variance between the front and rear axles. Any such mechanism would, however, continue to apply relatively heavy power to both axles. Enough power to cause the steering of the vehicle to swing back and forth in tight, slow turning maneuvers. This power would also creat unnecessary load on U-joints, gears and bearings. It remains then that inadvertent engagement and operation of a four-wheel drive vehicle in its four-wheel drive mode on dry or hard pavement would cause major damage to the vehicle drive train.
This problem sometimes exists because the transfer case remains "gear bound" even after the driver has attempted to disengage the front drive shaft.
The present invention provides an apparatus for sensing and indicating the status of the front driving axle, or any axle, without requiring the vehicle occupants to stop the vehicle and perform a visual inspection of the vehicle drive train. Consequently, the present invention provides the driver with a warning indicator that enables him to shift from four-wheel drive mode prior to damaging the vehicle drive train.